H-k-atpase activity in pna-binding intercalated cells of newborn
rabbit cortical collecting duct.
Constantinescu, Alexandru, Randi B. Silver, and Lisa M. Satlin.
Department of Pediatrics, Albert Einstein College of Medicine, 1410
Pelham Pkwy South, Bronx, N.Y. 10461, Department of Physiology,
Cornell University Medical College, 1300 York Ave., New York, N.Y.
10021
APStracts 3:0176F, 1996.
Functional and immunocytochemical studies indicate that intercalated
cells in the adult rabbit cortical collecting duct (CCD) possess an
H-K-ATPase. Because growing subjects must retain K+ and excrete H+,
we sought to determine whether H-K-ATPase is present in the CCD early
in life and, if so, assess its activity and polarity. H-K-ATPase
activity was defined as the initial rate of SCH 28080-inhibitable K+
-dependent cell pH (pHi) recovery observed, in the absence of Na+, in
response to an in vitro acid load. Transporter activity was assayed
in intercalated cells labeled with the pH sensitive dye BCECF and
apical cell surface marker rhodamine peanut lectin (PNA) in split
-open CCDs isolated from neonatal and adult NZW rabbits. In Na+-free
HEPES buffered solutions (nominal absence of CO2/HCO3-), the rate of
K+-dependent pHi recovery from a NH4Cl-induced acid load was similar
in newborn (0.056+/-0.015 pH U/min; n=9) and adult (0.060+/-0.019 pH
U/min; n=9; p=NS) cells. This rate of K+-dependent pHi recovery was
significantly reduced by 10-20 [mu]M SCH 28080, an inhibitor of
gastric H-K-ATPase, in both newborns (0.009+/-0.003 pH U/min; n=7)
and adults (0.013+/-0.007 pH U/min; n=9)(p<0.05 compared to
rates in absence of inhibitor). To determine whether the location of
the transporter is consistent with a role in K+ absorption and H+
secretion, pHi recovery of acutely acid-loaded intercalated cells in
neonatal CCDs (n=7) microperfused and bathed in the absence of Na+
and K+ was monitored after selective addition of K+ to either the
luminal or basolateral membrane. Addition of 5 mM K+ led to a
significantly greater rate of pHi recovery when it was added to the
luminal than the peritubular solution (0.049+/-0.005 vs. 0.018+/
-0.005 pH U/min; p<0.05). We conclude that PNA-binding
intercalated cells of the neonatal CCD possess H-K-ATPase activity,
predominantly located in the apical membrane. This provides a
mechanism for H+ secretion and K+ retention, processes required for
growth.
Received 25 January 1996; accepted in final form 19 September
1996.
APS Manuscript Number F28-6.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996